Field of the Invention and Related Art Statement
The present invention relates to a recording and reproducing apparatus using opto-magnetic discs, and more particularly to an apparatus for recording and/or reproducing a real time signal such as a television signal by using the opto-magnetic disc.
The opto-magnetic disc has been used to record a new information signal be erasing a previously recorded information signal. The erasing operation is carried out by projecting a light beam spot upon the disc, while the disc is subjected to an erasing bias magnetic field having a predetermined first direction. During the recording operation, the disc is subject to a recording bias magnetic field having a second direction opposite to said first direction and the light beam spot whose intensity is modulated in accordance with the information signal to be recorded is projected upon the opto-magnetic disk. In this manner, in order to effect the recording in the known apparatus it is necessary to trace an information track on the disc twice. Therefore, it is impossible to record a real time signal such as a television signal. Further, in case of effecting the reproduciton, since the opto-magnetic head needs a rather long access time of at least several hundreds milliseconds, there would be produced a time gap from an end of the reproduction of a certain event to a start of the reproduction of a next event, so that the continuous reproduction could not be performed.
In the known apparatus, the television signal of one frame or field is recorded on one turn of the information track on the opto-magnetic disc. In case of effecting the reproduction in a special mode such as a slow motion mode, the track jump is carried out during a vertical blanking period of the television signal. Then, it is apparent that the record density is reduced due to the fact that the blanking period is also recorded on the disc.
In the known apparatus in which the revolution velocity of the opto-magnetic disc is remained constant, the record density in an outer region of the disc is smaller than that in an inner region and thus the total record density is rather low. It is also known to vary the rotating velocity of the disc is changed in accordance with positions thereon such that the record density is remained constant all over the record region of the disc. However, in such an apparatus, it is difficult to achieve the high speed access and special mode of reproduction, because the television signal of one frame or field is no more recorded on one turn of the information track.